The Animal Resources Core (Core A) will provide young and middle age Sprague-Dawley rats of defined ovarian status used by all projects. Daily vaginal cytology will identify middle-aged irregular cyclers as a perimenopausal model. Some animals will be OVX and given replacements of estradiol (E2) with or without progesterone (P4). Necropsy will identify gross organ pathology, e.g. pituitary tumors. All projects also use the Alzheimer disease (AD) triple transgenic Alzheimer mouse: females of different ages will be OVXs and given steroid replacements. Tissues will be collected and deposited into storage managed by the Analytic Core. Blood will be given to the Analytic Core to be assayed for E2 and P4. A main goal of the animal core is the development of the rodent perimenopause and menopause model. These latter animal models will be crucial in determining the impact of reproductive aging on the neural responses to hormone therapy.